The quantitative estimation of metals based on chromatographic separation

Abstract

A literature survey showed that metals may be estimated both by column chromatography and by many methods employing paper chromatography, including removal of the metal from the paper, direct comparison, measurement of spot size. Radioactivity methods, and particularly by photometric estimation directly on paper. Photometric estimations on paper present many practical advantages, but require careful standardisation of conditions. Factors affecting the production of reproducible chromatograms and the principles of photometric estimation on paper are discussed. The object of the experimental work was to study spectrophotometric methods of estimation directly on paper. A method of ensuring complete and reproducible development of copper and nickel by rubeanic acid is described. The lack of uniformity of paper by transmitted light is shown to be much more apparent than by reflected light and this suggests that very small scanning areas should not be used in transmission work. It is shown that, even when slits as large as 15sq. mm. are used in the estimation of non-chromatographed spots, results based on reflection are more precise than those based on transmission. Rendering the paper transparent appeared to present some advantages both in reflection and in transmission work, but measurements on dry paper were found to be more suitable for routine use. Chromtograms run on narrow strips were scanned by transmission and estimated both by a minimum transmittance method and by a method involving interrogation of the total quantity of substance in the spot. Chromatograms run on broad rectangular sheets were estimated by a minimum reflectance method. This method was used in preference to the transmission methods of analysis. The recommended method of estimating 0.25 to 2.5μg of copper to an accuracy ± 5% in the presence of relatively large quantities of nickel, mercuric mercury, cadmium, and bismuth, involves separation by descending chromatography using butanol 3 N HCl, development in rubeanic acid, cutting out the spots, measuring the reflectance at their centre at 660 mμ